A physics professor at a leading Taiwanese university has led a group of researchers in developing a recordable optical disk capable of packing in 100 Gbytes of data and slipping into a pants pocket. The disk is compatible with today's CD and DVD technology, running off the same red laser pick-up heads used in a typical disk player.

To achieve the 100-Gbyte density target, the research team at National Taiwan University, led by professor Tsai Din Ping, used near-field optics — where the distance used for the interaction of the laser and media is shorter than the wavelength of light used to make the recording marks on the disk.

Two layers were added to the disk to achieve the near-field effect. The first is a transparent dielectric spacing layer, about 20 nanometers to 40 nanometers thick, which keeps the distance constant in the near field. The other layer is an active layer, which will interact with the focus point of the laser beam, generate the near-field effect and then transfer the mark to the recording layer.

Smaller mark

Using a standard sized disk, 12 centimeters in diameter, the researchers drew down the mark size to about 100 nm, less than about 400 nm for today's DVDs and 900 nm for CDs. "Even with such a small mark size, we can still have about 35 dB on the readout signal," Tsai said. "If you check your DVD disk today, the readout range is about the same, from 30 dB to 40 dB. So that's a very good result because the mark size is much smaller than 400 nm but the carrier-to-noise ratio is still very good. That's not easy."

Japanese companies and university researchers have also been developing high-density prototypes. Matsushita Electric Industrial Co. Ltd. developed a dual-layer rewritable optical disk last year that could store 50 Gbytes per side, enough for four hours of high-definition movies. It used violet lasers, however, not red lasers.

Tsai said his prototype is ready to hit the market today, but Wang doubts the market is ready. The disk may be capable of recording dozens of Star Trek episodes, but there aren't any drives available to utilize it and no one is working on one. Such systems would also require a new chip set. "Today's technology still has a ways to go before this is needed," Wang said.

In the meantime, Wang said Ritek should work on polishing the signal-to-noise characteristics on disks in the 40-Gbyte to 60-Gbyte range, which would still far outstrip today's 9.4-Gbyte maximum capacity for a dual-sided, dual-layer DVDs. Even next-generation proposals, such as Blu-ray DVDs, top out at about 27 Gbytes. Besides, they use pricier technology — they are based on blue lasers — that is not backward compatible with today's red laser standard. "The next two years will be very important for this technology," Wang said. "If we can get through the big breakthroughs we need, this will be a threat to Blu-ray."

During that time, however, Tsai will be prodding his team to push the limits of density even further. Ritek and Taiwan's National Science Council are funding the research until February 2003 with $660,000 — the project started in March 2000. "Our goal is to make an even smaller mark size that will still be stable within the near field. To do this, we will have to find a nanostructure to make this happen in a much easier way," Tsai said.

"One hundred gigabytes is not the limit; it is just the beginning. Our goal is terabit," he said.